1. Field
Exemplary embodiments of the present invention relate to a complementary metal oxide semiconductor (CMOS) image sensor and, more particularly, to a ramp signal generator having a voltage overlapping function and noise cancellation in a CMOS image sensor.
In the embodiments of the present invention, as an example, replica noise that copies pixel power noise will be discussed. Power noise is one of main contributors to the horizontal noise generated in a CMOS image sensor. In the embodiments, replica noise copying the power noise of a pixel is overlapped with a ramp signal through a voltage overlapping function. However, the applications of the present invention are not limited to this example.
2. Description of the Related Art
In the typical column parallel structure of a CMOS image sensor, noise may be generated due by the supply voltage the read-out circuit comparators, which operate in differential mode, and may be effectively removed through operations in a common mode.
However, since power noise generated from a pixel may be contained in a pixel signal and then applied to the read-out circuit, the power noise may not be removed through the read-out circuit, but may be contained in the outputted pixel data.
The power noise of the pixel may include supply power noise or ground power noise. Furthermore, the power noise may include supply power noise and ground power noise, which are overlapped through a specific circuit. In addition, the power noise may include all types of power noises generated from a pixel array.
Since power noise generated from a pixel array is a main contributor of overall noise, the power noise needs to be removed or suppressed as much as possible.